This invention concerns a process and an apparatus for determining optimal energy insertion into coagulating systems, particularly for precipitation, floccing, and sedimentation processes, by means of opacity measurements, so that, without great chemical, energy, and time expenditures, processes for precipitating, floccing and sedimentation, for example for preparation of drinking water or for cleaning industrial or communal sewage and similar processes in the chemical industry, can be designed, evaluated and optimized.
Known processes and apparatus to investigate precipitation, floccing (or coagulation), and sedimentation behavior have not taken into consideration kinetic energy which in actual processes is applied to fluid coagulating systems.
Because of rising demands for protecting the environment, increasing application is made of processes of precipitation neutralization, processes of floccing, and related processes of sedimentation for cleaning drinking water as well as for cleaning sewage, so as, for example, to eliminate phosphates from community-sector sewage or to remove heavy metals from industrial sewage.
To design new installations or to technically optimize processes of existing installations, because of the complexity of courses, or sequences, of such processes, it is essential to carry out, beginning with laboratory measures, tests with which technical parameters of the processes for operating the installations can be determined.
In addition to an analytical determination of materials contained in water before and after treatment, so-called series, or multiple, stirring works have been employed for decades in which simultaneous multiple tests under varying particular parameters were carried out (Haberer, K.: "Moeglichkeiten und Grenzen der Steurung von Flockungsanlagen," published by the Abteilung des Lehrstuhls fuer Wasserchemie, Pamphlet 3, Institut fuer Gastechnik, Foerderungstechnik und Wasserchemie of the Universitaet Karlsruhe, Karlsruhe, 1967/1).
The variation of a test parameter is limited in this exclusively to the amount of floccing compound. All additional test conditions are intentionally held constant. In particular, the mixing, or stirring, speed or stirring energy is not brought into consideration as an influential parameter. The described variations of rotational speed is in two steps, one for the usual method of floccing testing to first achieve a quick and uniform distribution of the floccing compound in the medium and, thereafter, one to maintain the uniform distribution. In each case the stirring rotational speed is held constant in each phase.
The evaluation of the precipitation, floccing, and sedimentation course thereby results mainly through subjective visual assessments using arbitrarily chosen rigged scales, which leads to tests which are carried out at different places by different people which cannot be compared. Thus, an actual documentation of an entire course of such a process is not thereby achieved.
In general, the employment of multiple stirring works, or devices, serves to allow a comparison of end results of tests which have been carried out in parallel. A change of the process parameter "mixing energy" is not achieved thereby. More importantly, only variations in the amount of concentration of floccing compound or auxiliary material are used.
Particle counting apparatus are further known with which the number and size of colloid particles can be determined when they flow through a test opening. These devices however fail when used with randomly divided flakes, or flocs, of various different structures and combinations, as they are in actual floccing processes.
Along the same lines, an apparatus is described by TANAKA AND MATSUBARA (Optical Absorption Studies of the Growth of Microcrystals in Nascent Suspensions, Silver Chloride Hydrosols, 1976, pg. 213-219 /2/) with which, by means of an optical sender and receiver, the light transmission of a fluid mixture, or solution, can be determined. With this apparatus an opacity measurement is carried out in which the height of the opacity limits is determined as a measure of the concentration of silver chloride in the solution. In order to distribute precipitated silver chloride uniformly in the suspension, a high-speed magnetic stirrer is used which inevitably breaks apart developing flakes to achieve a uniform distribution. In this respect, the authors themselves write that such an apparatus is only suitable for nascent liquid mixtures. By operation of the apparatus, an assessment of a beginning stage of a nucleating agent (the beginning of the peri-kenetic phase) is possible. A description of an entire precipitation, floccing, and sedimentation course, or sequence, in an actual fluid mixture (for example sewage) is not possible with this apparatus.
An evaluation of the floccing behavior at various points in an reaction container, for example at various heights, is also not possible with this arrangement.
A further method is described in German Offenglegungsschrift DE-OS 40 36 048 /3/ with which a determination of a foam height or sedimentation height in a fluid can result. The opacity increase of the optical density of foam and sedimentation borders serves thereby to provide a characteristic measurement for determining foam and sedimentation heights. Floccing and the sedimentation results without additional introduction of kinetic energy through only the force of gravity. With this process and the described apparatus therefor, only a determination of an end condition of a precipitation and sedimentation process is possible. Also, this described process requires at least two test runs carried out in series because first a calibration of the test arrangement and, only thereafter, an optical determination of the vertical layer borders (opacity increases) at foam and sedimentation layers must be carried out. A continuing analysis and documentation of the entire precipitation and floccing process is not possible with this solution. However, this process allows a determination of a speed of sedimentation and a height of the sedimentation in a reaction container.
In 1969, through HELMBOLDT AND VOGEL (Helmboldt, O.; Vogel, W.: Beurteilung von Flockungsvorgaengen, Wasser Luft und Betrieb 13 (1969) 5, pages 164-168) a substantial systematizing of the observation and documentation of precipitation, floccing, and sedimentation processes resulted, in that they described the optical manifestations of these processes by means of opacity measurements taken throughout an entire test run in a 600 mm becher glass. From obtained opacity curves, valuable conclusions as to the test parameters can be gained. From this the dynamic course, or sequence, of a precipitation, floccing and sedimentation process can be described as follows:
After the mixing of a floccing compound, with a conventional stirrer, into a liquid to be examined (so-called mixing phase) it (the mixture) enters a floccing phase in which there is intimate contact between the floccing compound and the suspended impurities. A distinct floccing increase leads to an increase in the opacity of the fluid. Thereby an increase in the opacity in relation to the beginning opacity serves as a measure of the intensity of the precipitation process. In a similar manner, a difference between the beginning and the end opacities is a measure of a cleaning effect. The schematic representation of the course, or curve, of opacity in an actual floccing process is represented in FIG. 1.
This analyzing method is burdened by a list of disadvantages:
For optimum floccing, conditions are assumed which create maximum large flocs, or flakes, which are maintained in suspension by insertion of appropriate stirring energy without, however, being destroyed by shearing forces created by the stirrer. This condition must be maintained in a stable manner over a sufficient time span to allow the flakes, or flocs, to partly absorb on their outer surfaces, from the surrounding fluid, released molecules as well as dispersed colloid particles, with the goal of achieving maximal cleaning effect. Because this optimum itself depends upon many parameters, such as concentration of the contained material, electrolyte content, concentration and insertion point-of-time of the precipitation, or floccing, compound, and the density and size of the flocs and because it can be shifted during the floccing process, it is often necessary with the above-described apparatus to have a large series of preliminary tests to approach an optimum energy insertion. To date, there are no known laboratory processes or apparatus which make possible optimizing floccing processes, relative to energy insertion, which are practically and technically controllable, and which react to changes in process parameters.
Theoretical calculations of an optimum energy insertion using opacity measurements are not possible because of the various characteristics of water contained materials with regard to its chemical composition, their various sizes concentrations, and colors, their various geometrical shapes, their various and different basic characteristics and their variety of different physical-chemical parameters.
A controlling of temperature by means of a thermostat on a test reactor, and thereby the possibility of carrying out comparative tests at various temperatures, was not realizable by Helboldt and Vogel without disturbing feedback effects on the measured results because, upon transmitting light through a sleeve about the reactor and a thermostatic liquid, the intensity of a light beam would be falsified, particularly by means of such influences as opacity and pollution of the thermostatic liquid and gradually appearing sedimentation on an inner surface of the sleeve of the thermostatic container, which would lead to unreproducible measured results.
Upon very voluminous flocculation the upper sedimentation border remains over a fixedly installed light gate, which obstructs transmission of the light. An evaluation in a test, with such a total extinction, is no longer possible.
In addition to the precipitation, floccing, and sedimentation, a process engineer is also interested in the characteristics of the flakes, or flocs, which, for example, for a specific filter counter-resistance finds its expression as an important characteristic for the drainage of sediment. For such an investigation, withdrawal of the sediment is necessary. The sucking out the flocs sediment by means of a syphon or pipette from a floor of a becher glass leads however, through the appearance of shearing forces, to an intermediate destruction of the flocs which, when stationary, can build themself back, however, in the rule they then display other geometry and changed characteristics.
Normal laboratory stirrers, in leaf or propeller form, lead to the appearance of substantially higher energy, or shear, gradations in areas of stirring edges than at areas spaced large distances from the stirring element, for example near a container wall or at a floor space of a reactor. This can lead to, already during the floccing process, a partial, and partly irrevsible, breaking up of the flocs. Because of this, the characteristics of the flocs sediment, have a negative influence on the drainability and absorption properties for other released or colloidal distributed water contained materials.
It is an object of this invention to provide a process and a measuring apparatus for carrying it out which make possible the duplication of complex dynamic precipitation, floccing and sedimentation processes as well as the analyzing, and the optimizing of relevant process parameters thereof. At the same time, a transferring of the resulting optimized process parameters to small as well as to large technical processes should be possible.